Diabetes mellitus is a disorder of carbohydrate metabolism, i.e. a syndrome characterized by hyperglycemia resulting from absolute or relative impairment in insulin secretion and/or insulin action.
Classification of Diabetes mellitus is based on the one adopted by the National Diabetes Data Group and WHO. Previously, it was based on age at onset, duration, and complications of the disease. Gestational diabetes mellitus is carbohydrate intolerance of variable severity with onset or first recognition during the current pregnancy. Patients with type I diabetes mellitus (DM), also known as insulin-dependent DM (IDDM) or juvenile-onset diabetes, may develop diabetic ketoacidosis (DKA). Patents with type II DM, also known as non-insulin-dependent DM (NIDDM), may develop nonketotic hyperglycemic-hyperosmolar coma (NKHHC). Common late microvascular complications include retinopathy, nephropathy, and peripheral and autonomic neuropathies. Macrovascular complications include atherosclerotic coronary and peripheral arterial disease.
Type I diabetes mellitus: Although it may occur at any age, type I diabetes mellitus most commonly develops in childhood or adolescence and is the predominant type of DM diagnosed before age 30. This type of diabetes accounts for 10 to 15% of all cases of DM and is characterized clinically by hyperglycemia and a propensity to diabetic ketoacidosis. The pancreas produces little or no insulin.
About 80% of patients with type I DM have specific HLA phenotypes associated with detectable serum islet cell cytoplasmic antibodies and islet cell surface antibodies (antibodies to glutamic acid decarboxylase and to insulin are found in a similar proportion of cases).
In these patients, type I DM results from a genetically susceptible, immune-mediated, selective destruction of >90% of their insulin-secreting cells. Their pancreatic islets exhibit insulitis, which is characterized by an infiltration of T lymphocytes accompanied by macrophages and B lymphocytes and by the loss of most of the beta-cells, without involvement of the glucagon-secreting alpha-cells. The antibodies present at diagnosis usually become undetectable after a few years. They may be primarily a response to beta-cell destruction, but some are cytotoxic for beta-cells and may contribute to their loss. The clinical onset of type I DM may occur in some patients years after the insidious onset of the underlying autoimmune process. Screening for these antibodies is included in numerous ongoing preventive studies.
Type II diabetes mellitus: Type II DM is usually the type of diabetes diagnosed in patients >30 years, but it also occurs in children and adolescents. It is characterized clinically by hyperglycemia and insulin resistance. Diabetic ketoacidosis is rare. Although most patients are treated with diet, exercise, and oral drugs, some patients intermittently or persistently require insulin to control symptomatic hyperglycemia and prevent nonketotic hyperglycemic-hyperosmolar coma. The concordance rate for type II DM in monozygotic twins is >90%. Type II DM is commonly associated with obesity, especially of the upper body (visceral/abdominal), and often present after a period of weight gain. Impaired glucose tolerance associated with aging is closely correlated with the typical weight gain. Type II DM patients with visceral/abdominal obesity may have normal glucose levels after losing weight.
Type II DM is a heterogeneous group of disorders in which hyperglycemia results from both an impaired insulin secretory response to glucose and decreased insulin effectiveness in stimulating glucose uptake by skeletal muscle and in restraining hepatic glucose production (insulin resistance). However, insulin resistance is common, and most patients with insulin resistance will not develop diabetes, because the body compensates by adequately increasing insulin secretion. Insulin resistance in the common variety of type II DM is not the result of genetic alterations in the insulin receptor or the glucose transporter. However, genetically determined post-receptor intracellular defects likely play a role. The resulting hyperinsulinemia may lead to other common conditions, such as obesity (abdominal), hypertension, hyperlipidemia, and coronary artery disease (the syndrome of insulin resistance).
Genetic factors appear to be the major determinants for the development of type II DM, yet no association between type II DM and specific HLA phenotypes or islet cell cytoplasmic antibodies has been demonstrated. An exception is a subset of non-obese adults with detectable islet cell cytoplasmic antibodies who carry one of the HLA phenotypes and who may eventually develop type I DM.
Before diabetes develops, patients generally lose the early insulin secretory response to glucose and may secrete relatively large amounts of proinsulin. In established diabetes, although fasting plasma insulin levels may be normal or even increased in type II DM patients, glucose-stimulated insulin secretion is clearly decreased. The decreased insulin levels reduce insulin-mediated glucose uptake and fail to restrain hepatic glucose production.
Hyperglycemia may not only be a consequence but also a cause of further impairment in glucose tolerance in the diabetic patient (glucose toxicity) because hyperglycemia decreases insulin sensitivity and increases hepatic glucose production. Once a patient's metabolic control improves the insulin or hypoglycemic drug dose is usually lowered.
Some cases of type II DM occur in young, non-obese adolescents (maturity-onset diabetes of the young [MODY]) with an autosomal dominant inheritance. Many families with MODY have a mutation in the glucokinase gene. Impairments in insulin secretion and in hepatic glucose regulation have been demonstrated in these patients.
Insulinopathies are rare cases of DM, with the clinical characteristics of type II DM, result from the heterozygous inheritance of a defective gene, leading to secretion of insulin that does not bind normally to the insulin receptor. These patients have greatly elevated plasma immunoreactive insulin levels associated with normal plasma glucose responses to exogenous insulin.
Diabetes may also be attributed to pancreatic disease: Chronic pancreatitis, particularly in alcoholics, is frequently associated with diabetes. Such patients lose both insulin-secreting and glucagon-secreting islets. Therefore, they may be mildly hyperglycemic and sensitive to low doses of insulin. Given the lack of effective counterregulation (exogenous insulin that is unopposed by glucagon), they frequently suffer from rapid onset of hypoglycemia. In Asia, Africa, and the Caribbean, DM is commonly observed in young, severely malnourished patients with severe protein deficiency and pancreatic disease; these patients are not prone to diabetic ketoacidosis but may require insulin.
Diagnosis of diabetes mellitus: In asymptomatic patients, DM is established when the diagnostic criterion for fasting hyperglycemia is met: a plasma (or serum) glucose level of >=140 mg/dl (>=7.77 mmol/l) after an overnight fast on two occasions in an adult or child.
An oral glucose tolerance test may be helpful in diagnosing type II DM in patients whose fasting glucose is between 115 and 140 mg/dl (6.38 and 7.77 mmol/L) and in those with a clinical condition that might be related to undiagnosed DM (e.g. polyneuropathy, retinopathy).
Treatment of diabetes mellitus: Hyperglycemia is responsible for most of the long-term microvascular complications of diabetes. It demonstrated a linear relationship between the levels of Hb A1c (see below) and the rate at which complications developed. Other studies have suggested that Hb A1c<8% is a threshold below which most complications can be prevented. Thus, therapy for type I DM should try to intensify metabolic control to lower Hb A1c while avoiding hypoglycemic episodes. However, treatment must be individualized and should be modified when circumstances make any risk of hypoglycemia unacceptable (e.g. in patients with a short life expectancy and in those with cerebrovascular or cardiac disease) or when the patient's risk of hypoglycemia is increased (e.g. in patients who are unreliable or who have autonomic neuropathy).
Diet to achieve weight reduction is most important in overweight patients with type II DM. If improvement in hyperglycemia is not achieved by diet, trial with an oral drug should be started.
The patient should be regularly assessed for symptoms or signs of complications, including a check of feet and pulses and sensation in the feet and legs, and a urine test for albumin. Periodic laboratory evaluation includes lipid profile, BUN (blood urea nitrogen) and serum creatinine levels, ECG, and an annual complete ophthalmologic evaluation.
Hypercholesterolemia or hypertension increases the risks for specific late complications and requires special attention and appropriate treatment. Although beta-adrenergic receptor blocking agents β-blockers, such as propranolol) can be used safely in most diabetics, they can mask the β-adrenergic symptoms of insulin-induced hypoglycemia and can impair the normal counterregulatory response. Thus, ACE inhibitors and calcium antagonists are often the drugs of choice.
Plasma glucose monitoring should be carried out by all patients, and insulin-treated patients should be taught to adjust their insulin doses accordingly. Glucose levels can be tested with easy-to-use home analyzers using a drop of fingertip blood. A spring-powered lancet is recommended to obtain the fingertip blood sample. The frequency of testing is determined individually. Insulin-treated diabetic patients ideally should test their plasma glucose daily before meals, 1 to 2 hours after meals, and at bedtime.
Most physicians periodically determine glycosylated hemoglobin (Hb A1c) to estimate plasma glucose control during the preceding 1 to 3 months. Hb A1c is the stable product of non-enzymatic glycosylation of Hb by plasma glucose and is formed at rates that increase with increasing plasma glucose levels. In most laboratories, the normal Hb A1c level is about 6%; in poorly controlled diabetics, the level ranges from 9 to 12%. Hb A1c is not a specific test for diagnosing diabetes; however, elevated Hb A1c often indicates existing diabetes.
Another test determines the fructosamine level. Fructosamine is formed by a chemical reaction of glucose with plasma protein and reflects glucose control in the previous 1 to 3 weeks. Therefore, this assay may show a change in control before Hb A1c and is often helpful when intensive treatment is applied and in short-term clinical trials.
As regards insulin treatment, human insulin is often preferred in initiating insulin treatment because it is less antigenic than animal-derived varieties. However, detectable insulin antibody levels, usually very low, develop in most insulin-treated patients, including those receiving human insulin preparations.
Insulin is routinely provided in preparations containing 100 U/ml (U-100 insulin) and is injected subcutaneously with disposable insulin syringes. The ½-ml syringes are generally preferred by patients who routinely inject doses of <=50 U, because they can be read more easily and facilitate the accurate measurement of smaller doses. A multiple-dose insulin injection device (NovolinPen), commonly referred to as an insulin pen, is designed to use a cartridge containing several days' dosage. Insulin should be refrigerated but never frozen; however, most insulin preparations are stable at room temperature for months, which facilitates their use at work and when traveling.
Diabetes may be associated with other endocrine diseases. Type II DM can be secondary to Cushing's syndrome, acromegaly, pheochromocytoma, glucagonoma, primary aldosteronism, or somatostatinoma. Most of these disorders are associated with peripheral or hepatic insulin resistance. Many patients will become diabetic once insulin secretion is also decreased. The prevalence of type I DM is increased in patients with certain autoimmune endocrine diseases, e.g. Graves' disease, Hashimoto's thyroiditis, and idiopathic Addison's disease.
Diabetes may also be induced by beta-cell toxins. Streptozotocin for instance can induce experimental diabetes in rats but rarely causes diabetes in humans.
Late complications of diabetes occur after several years of poorly controlled hyperglycemia. Glucose levels are increased in all cells except where there is insulin-mediated glucose uptake (mainly muscle), resulting in an increase in glycolysation and in the activity of other metabolic pathways, which may be caused by complications. Most microvascular complications can be delayed, prevented, or even reversed by tight glycemic control, i.e. achieving near-normal fasting and postprandial glucose levels, reflected by near-normal glycosylated hemoglobin (Hb A1c). Macrovascular disease such as atherosclerosis may lead to symptomatic coronary artery disease, claudication, skin breakdown, and infections. Although hyperglycemia may accelerate atherosclerosis, many years of hyperinsulinemia preceding the onset of diabetes (with insulin resistance) may play a major initiating role. Amputation of a lower limb for severe peripheral vascular disease, intermittent claudication, and gangrene remains common. Background retinopathy (the initial retinal changes seen on ophthalmoscopic examination or in retinal photographs) does not significantly alter vision, but it can progress to macular edema or proliferative retinopathy with retinal detachment or hemorrhage, which can cause blindness. About 85% of all diabetics eventually develop some degree of retinopathy. Diabetic nephropathy is usually asymptomatic until end-stage renal disease develops, but it can cause the nephrotic syndrome.
Diabetic neuropathy is a further complication of diabetes, but it is also common in connection with other diseases.
Multiple mononeuropathy is usually secondary to collagen vascular disorders (e.g. polyarteritis nodosa, systemic lupus erythematosus (SLE), Sjögren's syndrome, rheumatoid arthritis (RA)), sarcoidosis, metabolic diseases (e.g. diabetes, amyloidosis), or infectious diseases (e.g. Lyme disease, HIV infection). Microorganisms may cause multiple mononeuropathy by direct invasion of the nerve (e.g. in leprosy).
Polyneuropathy due to acute febrile diseases may result from a toxin (e.g. in diphtheria) or an autoimmune reaction (e.g. in Guillain-Barré syndrome); the polyneuropathy that sometimes follows immunizations is probably also autoimmune.
Toxic agents generally cause polyneuropathy but sometimes mononeuropathy. They include emetine, hexobarbital, barbital, chlorobutanol, sulfonamides, phenytoin, nitrofurantoin, the vinca alkaloids, heavy metals, carbon monoxide, triorthocresyl phosphate, orthodinitrophenol, many solvents, other industrial poisons, and certain AIDS drugs (e.g. zalcitabine, didanosine).
Nutritional deficiencies and metabolic disorders may result in polyneuropathy. B vitamin deficiency is often the cause (e.g. in alcoholism, beriberi, pernicious anemia, isoniazid-induced pyridoxine deficiency, malabsorption syndromes, and hyperemesis gravidarum). Polyneuropathy also occurs in hypothyroidism, porphyria, sarcoidosis, amyloidosis, and uremia.
Malignancy may cause polyneuropathy via monoclonal gammopathy (multiple myeloma, lymphoma), amyloid invasion, or nutritional deficiencies or as a paraneoplastic syndrome.
Polyneuropathy due to metabolic disorders, such as diabetes mellitus or renal failure, develops slowly, often over months or years. It frequently begins with sensory abnormalities in the lower extremities that are often more severe distally than proximally. Peripheral tingling, numbness, burning pain, or deficiencies in joint proprioception and vibratory sensation are often prominent. Pain is often worse at night and may be aggravated by touching the affected area or by temperature changes. In severe cases, there are objective signs of sensory loss, typically with stocking-and-glove distribution. Achilles and other deep tendon reflexes are diminished or absent. Painless ulcers on the digits or Charcot's joints may develop when sensory loss is profound. Sensory or proprioceptive deficits may lead to gait abnormalities. Motor involvement results in distal muscle weakness and atrophy. The autonomic nervous system may be additionally or selectively involved, leading to nocturnal diarrhea, urinary and fecal incontinence, impotence, or postural hypotension. Vasomotor symptoms vary. The skin may be paler and drier than normal, sometimes with dusky discoloration; sweating may be excessive. Trophic changes (smooth and shiny skin, pitted or ridged nails, osteoporosis) are common in severe, prolonged cases.
Treatment of the systemic disorder (e.g. diabetes mellitus, renal failure, multiple myeloma, tumor) may halt progression and improve symptoms, but recovery is slow. Entrapment neuropathies may require corticosteroid injections or surgical decompression. Physical therapy and splints reduce the likelihood or severity of contractures.
Diabetes mellitus can cause sensorimotor distal polyneuropathy (most common), multiple mononeuropathy, and focal mononeuropathy (e.g. of the oculomotor or abducens cranial nerves). Polyneuropathy commonly occurs as a distal, symmetric, predominantly sensory polyneuropathy that causes sensory deficits, which begin with and are usually marked by a stocking-glove distribution.
Generally, peripheral neuropathy is defined as a syndrome of sensory loss, muscle weakness and atrophy, decreased deep tendon reflexes, and vasomotor symptoms, alone or in any combination. The disease may affect a single nerve (mononeuropathy), two or more nerves in separate areas (multiple mononeuropathy), or many nerves simultaneously (polyneuropathy). The axon may be primarily affected (such as in diabetes mellitus, Lyme disease, or uremia or with toxic agents) or the myelin sheath or Schwann cell (such as in acute or chronic inflammatory polyneuropathy, leukodystrophies, or Guillain-Barré syndrome). Damage to small unmyelinated and myelinated fibers results primarily in loss of temperature and pain sensation; damage to large myelinated fibers results in motor or proprioceptive defects. Some neuropathies (e.g. due to lead toxicity, dapsone use, tick bite, porphyria, or Guillain-Barré syndrome) primarily affect motor fibers; others (e.g. due to dorsal root ganglionitis of cancer, leprosy, AIDS, diabetes mellitus, or chronic pyridoxine intoxication) primarily affect the dorsal root ganglia or sensory fibers, producing sensory symptoms. Occasionally, cranial nerves are also involved (e.g. in Guillain-Barré syndrome, Lyme disease, diabetes mellitus, and diphtheria).
Trauma is the most common cause of a localized injury to a single nerve. Violent muscular activity or forcible overextension of a joint may produce a focal neuropathy, as may repeated small traumas (e.g. tight gripping of small tools, excessive vibration from air hammers). Pressure or entrapment paralysis usually affects superficial nerves (ulnar, radial, peroneal) at bony prominences (e.g. during sound sleep or during anesthesia in thin or cachectic persons and often in alcoholics) or at narrow canals (e.g. in carpal tunnel syndrome). Pressure paralysis may also result from tumors, bony hyperostosis, casts, crutches, or prolonged cramped postures (e.g. in gardening). Hemorrhage into a nerve and exposure to cold or radiation may also cause neuropathy. Mononeuropathy may further result from direct tumor invasion.
Diabetic polyneuropathy may cause numbness, tingling, and paresthesias in the extremities and, less often, debilitating, severe, deep-seated pain and hyperesthesias. Ankle jerks are usually decreased or absent. Other causes of polyneuropathy must be excluded. Acute, painful mononeuropathies affecting the 3rd, 4th, or 6th cranial nerve as well as other nerves, such as the femoral, may spontaneously improve over weeks to months, occur more frequently in older diabetics, and are attributed to nerve infarctions. Autonomic neuropathy occurs primarily in diabetics with polyneuropathy and can cause postural hypotension, disordered sweating, impotence and retrograde ejaculation in men, impaired bladder function, delayed gastric emptying (sometimes with dumping syndrome), esophageal dysfunction, constipation or diarrhea, and nocturnal diarrhea. A decrease in heart rate response to the Valsalva maneuver or on standing and unchanged heart rate variation during deep breathing are evidence of autonomic neuropathy in diabetics.
Diabetic polyneuropathy is the major cause for foot ulcers and joint problems, which are important causes of morbidity in diabetes mellitus. In diabetic polyneuropathy, the sensory denervation impairs the perception of trauma from such common causes as ill-fitting shoes or pebbles. Alterations in proprioception lead to an abnormal pattern of weight bearing and sometimes to the development of Charcot's joints.
Patients with infected foot ulcers frequently feel no pain because of neuropathy and have no systemic symptoms until late in a neglected course. Deep ulcers and particularly ulcers associated with any detectable cellulitis require immediate hospitalization, since systemic toxicity and permanent disability may develop. Early surgical debridement is an essential part of management, but amputation is sometimes necessary.
Interleukin-6 (IL-6) is a multifunctional cytokine produced and secreted by several different cell types. This pleiotropic cytokine plays a central role in cell defense mechanisms including the immune response, acute phase response and hematopoiesis. IL-6 is a 20 to 26 kDa glycoprotein having 185 amino acids that has been cloned previously (May et al, (1986); Zilberstein et al, (1986); Hirano et al, (1986)). IL-6 has previously been referred to as B cell stimulatory factor 2 (BSF-2), interferon-beta 2 and hepatocyte stimulatory factor. IL-6 is secreted by a number of different tissues including the liver, spleen, and bone marrow and by a variety of cell types including monocytes, fibroblasts, endothelial, B- and T-cells. IL-6 is activated at the transcriptional level by a variety of signals including viruses, double stranded RNA, bacteria and bacterial lipopolysaccarides, and inflammatory cytokines such as IL-1 and TNF.
IL-6 has been implicated in the pathogenesis of human inflammatory CNS diseases. Increased plasma and cerebrospinal fluid levels of IL-6 have been demonstrated in patients with multiple sclerosis (Frei et al., (1991)), for instance.
Recent experiments on the effects of IL-6 on cells of the central and peripheral nervous system indicate that IL-6 may have protective effects on neuronal cells as well as some impact on inflammatory neurodegenerative processes (Gadient and Otten, 1997, Mendel et al, 1998). IL-6 was found to prevent glutamate-induced cell death in hippocampal (Yamada et al., 1994) as well as in striatal (Toulmond et al., 1992) neurons. In transgenic mice expressing high levels of both human IL-6 and human soluble IL-6R (sIL-6-R), an accelerated nerve regeneration was observed following injury of the hypoglossal nerve as shown by retrograde labeling of the hypoglossal nuclei in the brain (Hirota et al, 1996). Furthermore, there has been some evidence that IL-6 is implied in a neurological disease, the demyelinating disorder Multiple Sclerosis (MS) (Mendel et al., 1998). Mice lacking the IL-6 gene were resistant to the experimental induction of the disease. On the other hand, there have been reports indicating that IL-6 has a negative effect on neuronal survival during early post-traumatic phase after nerve injury (Fisher et al., 2001)
The biological activities of IL-6 are mediated by a membrane receptor system comprising two different proteins one named IL-6 receptor or gp80 and the other gp130 (reviewed by Hirano et al, 1994). gp130 is a transmembrane glycoprotein with a length of 918 amino acids, including an intracellular domain of 277 amino acids, is a subunit constituent of several cytokine receptors, including those for IL-6, IL-11, LIF, Oncostatin M, CNTF (ciliary neurotrophic factor), CT-1. IL-6 being the prototype of the cytokines acting through gp130, this cytokine family is also called “IL-6 type cytokines”.
gp130 participates in the formation of high-affinity receptors for these cytokines by binding to low affinity receptor chains. Accordingly, gp130 has been called also an “affinity converter”. Ligand binding to a cytokine receptor leads to the dimerization of gp130 (shown for the IL6 receptor) or heterodimerization (shown for LIF, Oncostatin M, and CNTF receptors) with a gp130-related protein known as the LIFRbeta subunit. Binding of the respective ligands is associated with the activation/association of a family of tyrosine kinases known as Janus kinases (JAKs), as the first step of intracellular signal transduction. Intracellular signaling processes include tyrosine phosphorylation and activation factors called STATs (signal transducer and activator of transcription).
The human gp130 gene product appears to be homologous to two distinct chromosomal loci on chromosomes 5 and 17. The presence of two distinct gp130 gene sequences is restricted to primates and is not found in other vertebrates.
It has been shown that the signaling activities of IL-6, IL-11, CNTF, Oncostatin M and LIF can be blocked specifically by different monoclonal antibodies directed against gp130. In addition to this, monoclonal antibodies, which directly activate gp130 independently of the presence of cytokines or their receptors have been found.
Other monoclonal antibodies directed against gp130 have been shown to inhibit IL-6-mediated functions. Soluble forms of gp130 (sgp130) with molecular masses of 90 and 110 Kda have been found in human serum. They can inhibit biological functions of those cytokines utilizing receptor systems with gp130 as a component.
Soluble forms of IL-6R gp80 (sIL-6R), corresponding to the extracellular domain of gp80, are natural products of the human body found as glycoproteins in blood and in urine (Novick et al, 1990, 1992). An exceptional property of sIL-6R molecules is that they act as potent agonists of IL-6 on many cell types including human cells (Taga et al, 1989; Novick et al, 1992). Even without the intracytoplasmic domain of gp80, sIL-6R is still capable of triggering the dimerization of gp130 in response to IL-6, which in turn mediates the subsequent IL-6-specific signal transduction and biological effects (Murakami et al, 1993). sIL-6R has two types of interaction with gp130 both of which are essential for the IL-6 specific biological activities (Halimi et al., 1995), and the active IL-6 receptor complex was proposed to be a hexameric structure formed by two gp130 chains, two IL-6R and two IL-6 ligands (Ward et al., 1994; Paonessa et al, 1995).
Chimeric molecules linking the soluble IL-6 receptor and IL-6 together have been described (Chebath et al., 1997, Fischer et al., 1997, WO 99/02552 and WO 97/32891). They have been designated IL-6R/IL-6 chimera and Hyper-IL-6, respectively, and will be called IL-6R/IL-6 in the following. The IL-6R/IL-6 chimera were generated by fusing the entire coding regions of the cDNAs encoding the soluble IL-6 receptor (sIL-6R) and IL-6 (Fischer et al., 1997; Chebath et al., 1997). Recombinant IL-6R/IL-6 chimera was produced in CHO cells (Chebath et al, 1997, WO99/02552). IL-6R/IL-6 chimera binds with a higher efficiency to the gp130 chain in vitro than does the mixture of IL-6 with sIL-6R (Kollet et al, 1999).